The invention relates to a hollow conduit for use in determining concentration profiles of liquid or gaseous materials along a route, wherein the conduit provided for accommodation of a testing medium, which latter is to be moved therethrough in chronological intervals and is to be guided past a detector, is designed so that the materials can penetrate into the interior of the conduit.
German Laid-Open Application No. 2,131,907 discloses a process and apparatus, with the aid of which concentration profiles of liquid and gaseous substances can be determined along a route in a relatively simple way with high precision. This method has found application, in particular, for monitoring leakage in crude oil and long distance gas pipelines. For this purpose, a hollow conduit is laid along the route (in the form of the long-distance pipeline), this conduit being fashioned so that the materials (i.e. the escaped crude oil or gas) can enter into the interior of the conduit. Preferably, a hose of a synthetic resin is employed, allowing the materials to diffuse into the interior of the conduit. This conduit is filled with a testing medium (for example air or, alternatively, water), and the column of this testing medium is pushed through the conduit in time intervals and guided past a detector sensitive to the materials. The position and extent of a leak can thus be perfectly determined.
The possibilities of utilizing the conventional method are affected by two circumstances: on the one hand, by an adequate size of the diffusion rate of the substances to be detected through the wall of the hollow conduit for the formation of the concentration profile to be evaluated and, on the other hand, by maintaining the amplitudes of the thus-formed concentration profile during the step of passing the medium through the conduit. The problem in this connection resides in that the materials available for the hollow conduit (synthetic resins), although possessing adequate diffusion characteristics, allow the escape, by diffusion, of many of the substances that have entered by diffusion, during the passing-through step to the detector. Consequently, some substances, such as, for example, benzene and diesel oil, already have disappeared from the testing medium after a brief travel route within the hollow conduit, and do not arrive at the detector. The conventional hollow conduits made of synthetic resins are useless, due to their lack of stability, for determination of concentration profiles at high ambient temperatures as well as under the effect of ionizing radiation--as is the case, for example, in the monitoring of superheated steam conduits in nuclear power plants.
It is an object of the invention to fashion the hollow conduit so that its wall absorption is reduced without at the same time appreciably impairing the entering diffusion process and that even concentration profiles in zones of high ambient temperatures and under the effect of ionizing radiation can be determined.
In order to attain the above-described object, the starting point is a hollow conduit designed so that the substances, the concentration profiles of which are to be determined, can penetrate into the interior of the conduit, and this object is attained by providing the conduit with openings spaced apart from one another, these openings being sealed with a material through which the substances can diffuse into the interior of the conduit.
Accordingly, the invention proposes to manufacture the hollow conduit so that it is built up of two different materials, rather than, as heretofore, with a homogeneous wall. The by far larger portion of the effective wall of the novel hollow conduit includes a compound having no absorptive properties and consequently being impermeable to the substances, while in case of the smaller portion, the openings, a different material becomes effective through which the substances can diffuse and enter into the interior of the conduit (penetrate thereinto by diffusion).
Since, while passing the testing medium through the hollow conduit fashioned according to this invention, the substances diffusing into the interior of the conduit through the openings come into contact almost exclusively with the wall of the conduit, which is impermeable to the substances, the latter can practically no longer escape by diffusion so that even for determining the concentration profiles of heretofore critical materials (benzene, diesel oil), the routes to be monitored can be of a length of several kilometers.
In an advantageous embodiment of the invention, a hollow inner conduit is provided in the interior of the conduit and in the longitudinal direction of the latter, the wall of this inner conduit exhibiting the openings and being made of a material impermeable to the substances, and the conduit is made of a flexible material through which the substances can diffuse into the interior of the conduit. Such a conduit, accordingly, consists of two layers: the outer layer made of a material through which the substances can enter by diffusion, and the inner layer is made of a material permitting no entrance by diffusion and therefore lacking also any absorptive properties--but yet exhibiting a plurality of small openings through which the substances that have diffused through the outer layer can penetrate into the interior of the conduit. In other words: the impermeable conduit provided with openings is sheathed by a hose of a permeable material.
Advantageously, the cross section of all openings of a section of the inner conduit is at least fifty times smaller than the outer surface area of this section. With such dimensioning, the escape of the substances by diffusion is extremely low.
It is suitable to provide that the inner conduit is in close contact with the inner wall of the conduit.
For reasons of economical manufacture, the inner conduit can be constituted by a spirally wound strip provided with cutouts along one of its longitudinal edges. These cutouts form the required openings.
The inner conduit consists advantageously of unplasticized polyvinyl chloride, a compound having practically no absorptive properties at all.
In a second embodiment of the invention, the conduit is a rigid pipe provided with the openings, with a wall impermeable for the substances, and the openings are sealed with the material through which the substances can diffuse into the interior of the conduit.
Advantageously, plugs serve for sealing the openings, these plugs being made of the material through which the substances can diffuse.
With the proviso that the pipe constituting the hollow conduit is made of a temperature-resistant material (heat-resistant synthetic resin or metal) and the plugs are porous ceramic and/or metallic sintered elements, the arrangement of this invention can just as well be utilized advantageously for determination of concentration profiles at relatively high and at high ambient temperatures, as well as under the effect of ionizing radiation--as is the case, for example, when monitoring superheated steam pipes in nuclear power plants.
In another embodiment of the invention, the openings are sealed by a wrapping, winding around the conduit, of a strip consisting of the material through which the substances can diffuse into the interior of the conduit.
The hollow conduit can also be a metallic corrugated pipe, sleeves being inserted at spacings in this pipe, carrying the openings sealed with the plugs. Such a conduit is advantageously utilized for the monitoring of pipe elbows of super-heated steam pipes, or such conduit can be readily placed in spiral form about a straight steam pipeline.
A conduit that can be manufactured economically and is simple in handling during installation is one which includes pipe sections, with the joints of these pipe sections serving as the openings, being closed off with hose sections made of the material through which the substances can diffuse into the interior of the conduit. Such a conduit is also capable of following along curved portions.
At ambient temperatures of up to 300 degrees Celsius, the plugs, the wrapping and/or the hose section preferably consist essentially of polytetrafluoroethylene, whereas polyethylene can be utilized at low temperatures.
The invention is illustrated in the appended drawings in six different embodiments which will be described in greater detail below. In the drawings: